The present invention relates generally to a method and apparatus for calendering a sheet material web, and in particular, to a method and apparatus for calendering a sheet material web while being carried by one or more carrier fabrics.
It is well known in the field of paper making, and particularly in the field of manufacturing tissue products such as facial tissues, bath tissues, paper towels and the like, to provide for a continuous running sheet material web to traverse an "open draw" before being wound into rolls. The area of open draw, where the dried sheet web is momentarily unsupported before being wound, can provide one location to calender the web, i.e., press the web to reduce the caliper or thickness thereof.
As described in U.S. Pat. No. 5,591,309, issued Jan. 7, 1997 to Rugowski et al., and U.S. Pat. No. 5,593,545, issued Jan. 14, 1997 to Rugowski et al., both assigned to Kimberly-Clark Corporation, the same assignee as the present application, open draws are a frequent source of sheet breaks and associated production delays. As a result, tissue sheets often are designed to have high machine direction strengths in order to remain intact as they are pulled through the open draw. However, high machine direction strengths can adversely affect the quality of the web in terms of its desired softness. Therefore, as explained in U.S. Pat. Nos. 5,591,309 and 5,593,545, the elimination of open draws in the tissue manufacturing process can result in a sheet material being made more efficiently at less cost and with more desirable properties.
As a result of eliminating the open draw, the sheet material web is typically wound onto a roll and thereafter subjected to a calendering operation in a subsequent converting or finishing process. Often, the sheet material web, such as that made by the uncreped through-air-dried (UCTAD) process described in U.S. Pat. Nos. 5,591,309 and 5,593,545, will have a relatively high bulk, with the attendant benefits of increased absorbency and improved fiber utilization. In order to achieve certain operating efficiencies, however, the high-bulk sheet material web typically must be wound onto relatively large diameter rolls. Without adequate yardage deposited on each roll, the time increment between the changing of the windup rolls can sometimes be too short from a logistic and resource management standpoint.
However, large diameter rolls, comprised of relatively loosely wound high bulk basesheets that may be susceptible to shifting between layers, may require special handling at the windup reel, during transportation from the reel to the converting or finishing stations, and/or during the converting and finishing process. For example, larger spaces may be required for interim storage, passageways between lines may need to be expanded and additional personnel and lift trucks may be needed for transportation. Moreover, line speeds at the converting and finishing lines may need to be reduced to minimize the risks typically associated with unwinding loosely wound rolls having low interlayer pressures.